The present invention relates to exchange network systems and, more particularly, to logical connection control systems capable of ready realization of a redundant structure for improving the reliability of logical connection used for communication between exchanges.
In prior art logical connection based on a common line signal system, for instance, link control is executed between data transfer circuits via an exclusive digital line. Therefore, for providing mutual logical connection among a plurality of exchanges, it is necessary to provide a data transfer circuit for each exchange. In addition, in many common line signal systems, a function of transferring control data via a CPU (i.e., software processing) in each exchange is defined.
In the prior art, however, as described above link control of logical connection is executed only between data transfer circuits connected to each other via an exclusive digital line. Therefore, where a plurality of exchanges are present, a data transfer circuit is necessary for each exchange, thus leading to corresponding cost increase and complicating the hardware structure.
Furthermore, although in the above common line signal system the control data transfer function is defined, logical connection is established only between data transfer circuits (i.e., between exchanges). Therefore, for the transfer of control data, the processing is performed via the CPU (i.e., software processing) in each exchange, thus necessitating extra loading of the CPU in each exchange.
The present invention was made in view of the above background, and it has an object of providing a logical connection control system, which permits readily realizing a logical mesh structure without unnecessary loading to the CPU in each exchange, thus improving the system maintenance and the reliability of the logical connection.
According to the present invention, an interface connected to a local area network is mounted in a data transfer circuit for establishing a logical inter-exchange connection such that it can connect a plurality of data transfer circuits provided in an exchange to one another. Thus, individual data transfer circuits can jointly establish logical inter-exchange connection. It is thus possible to to readily realize logical connection, which is simple in physical hardware constitution and realizes a logical mesh structure. In addition, since a plurality of data transfer circuits can be connected to one another by the local area network interface, when a data transfer circuit receives data to be transferred to a different exchange from its own, the load of the CPU (i.e., software processing) in the own exchange can be alleviated by the execution of a process of data transfer between the data transfer circuits by using the local area network side interface.
According to an aspect of the present invention, there is provided a logical connection control system, that is, in an exchange network having a plurality of exchanges, a logical connection control system, wherein each exchange includes an exchange execution unit, a communication control unit for controlling the execution of communication between exchanges and a logical connection control circuit for establishing a route for exchanging control data with a different exchange, and can establish logical connection between exchanges for exchanging control data therebetween.
The communication control unit has a function of updating routing data according to the status of establishment of logical connection from the logical connection control circuit to each exchange, a function of storing the routing data in a routing data control circuit and a function of communicating with a different exchange via the logical connection control circuit.
Each exchange includes two communication control drivers for establishing logical connection between exchanges that is necessary when transmitting data to a different exchange under control of an instruction from the communication control unit, and the logical connection control unit has a function of determining, according to routing data, which one of the two communication control drivers is to be used.
An interface of a local area network connects each communication control driver via a local area network connector to a plurality of data transfer circuits.
Each exchange includes a plurality of data transfer circuits each having two different interfaces, one connected to an exclusive digital line and the other connected to a local area network, and the communication control unit can be connected to a data transfer circuit in a different exchange via a pertinent exclusive digital line while being connected to all the data transfer circuits in the own exchange via the local area network.
Each data transfer circuit has a function of communicating with a data transfer circuit in a different exchange via the exclusive digital line interface and receiving various states of the data transfer circuit in the different exchange.
The communication control unit has a function of distributing routing data stored in the routing data control circuit to all the data transfer circuits in the own exchange via the local area network interface.
When the data transfer circuit receives data transmitted from a different exchange via an exclusive digital line, it refers to destination exchange identification number contained in the received data and, if the received data is destined to a different exchange, determines, from routing data having been distributed from the communication control unit and held in it, the destination data transfer circuit, thus permitting direct transmission and reception of data between the data transfer circuits without agency of the control of the exchange execution unit in each exchange but via the local area network interface.
When no data transfer circuit in a different exchange which is found as a data relay destination in the own local area network is present, the data transfer circuit informs the communication control unit in the own exchange that no relay destination is present.
Wherein when the communication control unit is informed from the data transfer circuit that no relay destination is present, it retrieves, with reference to routing data stored in the routing data control circuit, for a data transfer circuit, which is present as a delay destination in a different local area network from the one of the informing data transfer circuit and, if such a relay destination data transfer circuit is present, secures communication between the exchanges by transmitting data to the relay destination data transfer circuit.
According to another aspect of the present invention, there is provided a logical connection control system, wherein an interface connected to a local area network is mounted in a data transfer circuit for establishing connection between exchanges, and a plurality of data transfer circuits mounted in the own exchange are connected one another via the local area network interface, thus providing a logical mesh structure about logical connection of exchanges to one another.
According other aspect of the present invention, there is provided a logical connection control system, wherein an interface connected to a local area network is mounted in a data transfer circuit which establishes connection between exchanges, and a plurality of data transfer circuits mounted in the own exchange are connected one another via the local area network interface one another, so that it can be used, when a data transfer circuit receives data to be transferred to a different exchange, for a process of data transfer between the data transfer circuits.
Other objects and features will be clarified from the following description with reference to attached drawings.